Lever plate in vgs type turbocharger and method of manufacturing the same

ABSTRACT

An object of the present invention is to provide a novel method of manufacturing a lever plate that is made of a material having a relatively small thickness but nonetheless has an engaging protrusion having an adequate thickness and an adequate height. 
     A lever plate in a VGS type turbocharger according to the present invention is a lever plate that is incorporated in an exhaust guide assembly in a VGS type turbocharger. The lever plate has a fitting hole into which a shaft part of the adjustable vane is fitted formed at a position close to one end of an elongated plate main body thereof and an engaging protrusion to be engaged with the drive ring formed at the other end thereof. The engaging protrusion is formed by bending a blanking material having the shape of an elongated flat plate. The engaging protrusion is pressed in a direction of raising thereof so as to have a thickness greater than the thickness of the plate main body of the lever plate, and opposite side peripheries of the engaging protrusion are subjected to finish blanking to have an arc shape.

TECHNICAL FIELD

The present invention relates to a lever plate that is a part of anadjustable mechanism that appropriately rotates an adjustable vane toadjust the flow rate of exhaust gas fed to a turbine in a variablegeometry system (VGS) type turbocharger used for an automobile engine orthe like. In particular, it relates to a novel lever plate that isreduced in weight and improved in precision and a method ofmanufacturing the same.

BACKGROUND ART

A turbocharger is one of known superchargers that are used as means forenhancing power and performance of an automobile engine. Theturbocharger is an apparatus that uses the energy of the exhaust gas ofthe engine to drive a turbine to rotate a compressor, thereby achievinga supercharged state in the engine that cannot be achieved by naturalaspiration. However, when the engine runs at low speed, the exhaust flowrate is also low, and therefore, the turbine rotor does notsatisfactorily rotate. Therefore, in a high-speed engine, theturbocharger has a disadvantage that the turbocharger takes a long timeto efficiently drive the turbine and requires a certain time, aso-called turbo lag, to speed up the engine after that, for example. Inaddition, in a low-speed, diesel engine, the turbocharger has adisadvantage that it is difficult to provide the turbo effect.

To overcome the disadvantages, a VGS type turbocharger (VGS unit) thatcan efficiently operate even at low rotational speeds has beendeveloped. When the engine runs at low speed, the VGS type turbochargerappropriately constricts the reduced flow of the exhaust gas withadjustable vanes (wings) to increase the velocity of the exhaust gas,thereby increasing the work of the turbine rotor, so that the VGS typeturbocharger can achieve high power even when the engine runs at lowspeed. Therefore, the VGS unit additionally requires an adjustmentmechanism for the adjustable vanes or the like, and thus the peripheralcomponents are also inevitably complicated in configuration or the likecompared with the conventional ones.

In view of such circumstances, the applicant also has been committed toresearch and development of the VGS type turbocharger and applied formany patents (see Patent Literature 1 to 8, for example).

The exhaust guide assembly of the VGS type turbocharger has anadjustment mechanism that includes a drive ring for uniformly openingand closing a plurality of adjustable vanes arranged at regularintervals in a circular configuration. The adjustment mechanism isconfigured so that the drive ring is driven to rotate by an externalactuator, a lever plate transfers the rotational movement of the drivering to the plurality of adjustable vanes to concurrently and uniformlyopen or close (rotate) the adjustable vanes. The adjustable vanes and amechanism for moving the adjustable vanes will be described in moredetail below. As schematically shown in FIG. 1, a number of adjustablevanes 1 are arranged in a circular configuration. A lever plate 5 isfixed at one end thereof to one end of the shaft part of each adjustablevane 1 like a crank. The lever plate 5 is engaged with an actuatingdrive ring 31 at the other end like a link. Rotation of the drive ring31 causes rotation of the lever plate 5 about the shaft of theadjustable vane 1, thereby changing the angle of the adjustable vane 1.

There are various types of conventional lever plates. FIG. 8 shows anexample of such conventional lever plates. A conventional lever plate105 has an elongated plate main body 151, a fitting hole 152 into whichthe shaft part of the adjustable vane is fitted formed in the plate mainbody 151 at one end thereof, and an engaging protrusion 153 to beengaged with the drive ring formed on the plate main body 151 at theother end thereof. When the lever plate is molded by plastic working,the engaging protrusion is formed by raising a part of the plate mainbody. Therefore, the material of the lever plate prepared has athickness t0 enough to accommodate for the working. As a result, thereare technical difficulties in reducing the weight of the lever plate 105and in piercing the thick member to form the fitting hole 152 for fixingthe shaft part of the adjustable vane, for example. More specifically,it is difficult to choose an appropriate piercing punch for forming thehole. In addition, even if the piercing can be successfully done, thepiercing punch wears out quickly because of the high load of theworking, and as a result, the cost of maintenance or the like of theentire manufacturing apparatus cannot be reduced satisfactorily. Inaddition, of course, if maintenance is inadequate, the precision of themanufactured product is inevitably lowered.

In addition, the engaging protrusion, which is the most importantfunctional part, is restricted by the thickness of the material, andtherefore, the height of the engaging protrusion required to ensure thereliable engagement cannot be arbitrarily set.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Patent Laid-Open No. 2003-49655

Patent Literature 2: Japanese Patent Laid-Open No. 2003-49663

Patent Literature 3: Japanese Patent Laid-Open No. 2003-49656

Patent Literature 4: Japanese Patent Laid-Open No. 2003-49657

Patent Literature 5: Japanese Patent Laid-Open No. 2003-49658

Patent Literature 6: Japanese Patent Laid-Open No. 2003-49659

Patent Literature 7: Japanese Patent Laid-Open No. 2003-48033

Patent Literature 8: Japanese Patent Laid-Open No. 2003-49660

SUMMARY OF INVENTION Technical Problem

The present invention has been devised in view of such circumstances,and an object of the present invention is to provide a novel method ofmanufacturing a lever plate that is made of a material having arelatively small thickness but nonetheless has an engaging protrusionhaving an adequate thickness and an adequate height.

Solution to Problem

A lever plate in a VGS type turbocharger according to claim 1 is a leverplate that is incorporated in an exhaust guide assembly in a VGS typeturbocharger, the exhaust guide assembly allows an engine to achieve ahigh power even when the engine runs at a low speed by rotating aplurality of adjustable vanes arranged at positions surrounding aturbine rotor by transferring a shifting of a drive ring to theadjustable vanes via lever plates,

appropriately constricting a relatively small amount of exhaust gasdischarged from the engine with the adjustable vanes to increase thevelocity of the exhaust gas, rotating the turbine rotor with the energyof the exhaust gas, and feeding an amount of air equal to or larger thanthe amount of air fed by natural aspiration to the engine with acompressor directly connected to the turbine rotor,

wherein the lever plate is made of an austenite-based heat resistingsteel and has a fitting hole into which a shaft part of the adjustablevane is fitted formed at a position close to one end of an elongatedplate main body thereof and an engaging protrusion to be engaged withthe drive ring formed at the other end thereof,

said engaging protrusion is formed by bending a blanking material havingthe shape of an elongated flat plate, and

the engaging protrusion is pressed in a direction of raising thereof soas to have a thickness greater than the thickness of the plate main bodyof the lever plate, and opposite side peripheries of the engagingprotrusion are subjected to finish blanking to have an arc shape.

A lever plate in a VGS type turbocharger according to claim 2 is thelever plate according to claim 1, in which said fitting hole is formedby piercing at the same time as the finish blanking of said engagingprotrusion.

A method of manufacturing a lever plate in a VGS type turbochargeraccording to claim 3 is a method of manufacturing a lever plate that isincorporated in an exhaust guide assembly in a VGS type turbocharger,the exhaust guide assembly allows an engine to achieve a high power evenwhen the engine runs at a low speed by rotating a plurality ofadjustable vanes arranged at positions surrounding a turbine rotor bytransferring a shifting of a drive ring to the adjustable vanes vialever plates,

appropriately constricting a relatively small amount of exhaust gasdischarged from the engine with the adjustable vanes to increase thevelocity of the exhaust gas, rotating the turbine rotor with the energyof the exhaust gas, and feeding an amount of air equal to or larger thanthe amount of air fed by natural aspiration to the engine with acompressor directly connected to the turbine rotor,

wherein the lever plate is made of an austenite-based heat resistingsteel and has a fitting hole into which a shaft part of the adjustablevane is fitted formed at a position close to one end of an elongatedplate main body thereof and an engaging protrusion to be engaged withthe drive ring formed at the other end thereof,

in a blanking step, a blank workpiece is obtained by punching anelongated flat plate out of a material having substantially the samethickness as the plate main body,

then in a bending step, the elongated blank workpiece is bent and raisedat substantially 90 degrees at one end to form a bent intermediateworkpiece having an uncompleted engaging protrusion part,

then in a crushing step, said uncompleted engaging protrusion part iscompressed in a direction of raising thereof to make the thickness ofthe said uncompleted engaging protrusion part greater than the thicknessof the plate main body to form a crushed intermediate workpiece,

then in a finish blanking step, a periphery of said crushed intermediateworkpiece is shaped by ironing to have the shape of a completed productto form a shaped workpiece, and

in a piercing step that precedes, is performed at the same time with orfollows said finish blanking step, the fitting hole is formed bypiercing in the plate main body at a position close to the end oppositeto the engaging protrusion to provide the completed product.

A method of manufacturing a lever plate in a VGS type turbochargeraccording to claim 4 is the method according to claim 3, in which saidfinish blanking step and said piercing step are performed at the sametime using the same die.

A method of manufacturing a lever plate in a VGS type turbochargeraccording to claim 5 is the method according to claim 3 or 4, in whichin said finish blanking step, opposite side peripheries of the engagingprotrusion formed on the crushed intermediate workpiece is worked to bean arc-shaped surface.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention configured as described in the claims solves theproblems described above.

Specifically, according to claim 1 of the present invention, advantagesdescribed below are provided.

The plate main body of the lever plate can be made of a relatively thinmaterial, while maintaining an adequate thickness of the engagingprotrusion of the lever plate. Therefore, the weight of the lever platecan be reduced. In addition, the fitting hole can be formed withoutapplying an excessive load, and as a result, the lever plate can bemanufactured with high precision.

In addition, the property of the engaging protrusion is modified owingto the process of forming the same. As a result, the resulting leverplate has significantly improved resistance against initial oxidationand initial abrasion.

According to claim 2 of the present invention, an advantage describedbelow is provided.

If the piercing to form the fitting hole in the lever plate and thefinish blanking of the whole of the lever plate including the engagingprotrusion are performed at the same time, the engaging protrusion andthe fitting hole can be precisely formed at the same positions as thoseon the die, and the lever plate can be manufactured with higherprecision.

According to claim 3 of the present invention, advantage described belowis provided.

Even when the plate main body of the lever plate is made of a materialhaving a relatively small thickness, the engaging protrusion of thelever plate can have a greater thickness. Therefore, the load appliedduring formation of the fitting hole can be prevented from beingexcessive, while reducing the weight of the lever plate. As a result,the lever plate can be manufactured with high precision.

In addition, the property of the engaging protrusion is modified owingto the process of forming the same. As a result, the resulting leverplate has significantly improved resistance against initial oxidationand initial abrasion.

According to claim 4 of the present invention, an advantage describedbelow is provided.

Since the finishing of the shape of the engaging protrusion of the leverplate and the formation of the fitting hole in the lever plate areperformed at the same time using the same die, the lever plate can bemanufactured with higher precision.

According to claim 5 of the present invention, an advantage describedbelow is provided.

The side periphery of the engaging protrusion of the lever plate canhave an appropriate arc-shaped surface owing to the finish blanking.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded perspective view showing an example of an exhaustguide assembly incorporating a lever plate according to the presentinvention.

FIG. 1( a) is a perspective view showing an example of a VGS typeturbocharger.

FIG. 1( b) is an enlarged perspective view showing the lever plateaccording to the present invention applied to the exhaust guideassembly.

FIG. 2( a) is an enlarged perspective view of the lever plate accordingto the present invention.

FIG. 2( b) is a partially cut-away side view of the lever plateaccording to the present invention.

FIG. 3 includes diagrams for illustrating a process of manufacturing thelever plate according to the present invention step by step.

FIG. 4 is a plan view for illustrating blanking in a case of aprogressing method.

FIG. 5 includes perspective views showing basic forms of a lever plateaccording to the present invention and a conventional lever plate forcomparison.

FIG. 6 is a graph showing a decrease in weight according to the presentinvention.

FIG. 7 is a graph showing relationships among the pressing ratio, thethickness of the material and the thickness of the engaging protrusionaccording to the present invention.

FIG. 8 includes a partially cut-away perspective view and a longitudinalcross-sectional view of a lever plate manufactured by a conventionalmethod.

DESCRIPTION OF EMBODIMENTS

Modes for carrying out the present invention include embodimentsdescribed below and various possible improvements thereof that fallwithin the technical spirit of the present invention.

In the following, an exhaust guide assembly AS in a VGS typeturbocharger C that incorporates an adjustment mechanism 3 to which alever plate 5 according to the present invention is applied will befirst schematically described, and then, the adjustment mechanism 3 andthe lever plate 5 will be described.

Embodiments

The exhaust guide assembly AS is used particularly to adjust the exhaustflow rate by appropriately constricting the flow of an exhaust gas Gwhen the engine runs at a low rotational speed. For example, as shown inFIG. 1, the exhaust guide assembly AS comprises a plurality ofadjustable vanes 1 that are arranged around a turbine rotor T andeffectively set the exhaust flow rate, a frame base 2 that rotatablyholds the adjustable vanes 1, and the adjustment mechanism 3 thatrotates the adjustable vanes 1 by a predetermined angle to appropriatelyset the flow rate of the exhaust gas G. In the following, thesecomponents will be described individually.

First, the adjustable vanes 1 will be described. As shown in FIG. 1 forpurposes of illustration, a plurality of adjustable vanes 1 is arrangedalong the outer periphery of the turbine rotor T in an arc configuration(in general, one exhaust guide assembly AS has 10 to 15 adjustable vanes1). The adjustable vanes 1 concurrently and generally uniformly rotateto adjust the exhaust flow rate. The adjustable vane 1 comprises a vanepart 11 and a shaft part 12. Next, these parts will be described.

The vane part 11 has a predetermined width that depends primarily on thewidth of the turbine rotor T and has an airfoil-shaped cross section ina direction perpendicular to the width direction so that the exhaust gasG is efficiently directed toward the turbine rotor T.

The vane part 11 has a flange part 13 having a slightly larger diameterthan the shaft part 12 at the boundary (connection) with the shaft part12 as required. The bottom surface (bearing surface) of the flange part13 is substantially flush with an end face of the vane part 11 andserves as a bearing surface when the adjustable vanes 1 are inserted inthe frame base 2 to restrict the position thereof with respect to theturbine rotor T in the width direction.

On the other hand, the shaft part 12 is integrally and seamlessly formedwith the vane part 11 and serves as a rotating shaft for moving the vanepart 11. The shaft part 12 has a reference surface 15 for attachment ofthe adjustable vane 11 formed at a tip end thereof. As described later,the shaft part 12 is fixed to the adjustment mechanism 3 at thereference surface 15 by caulking or the like. For example, two referencesurfaces 15 are formed by cutting the shaft part 12 at two oppositepositions as shown in FIG. 1.

The adjustable vane 1 shown in FIG. 1 is a so-called cantilever typeadjustable vane 1 that has the shaft part 12 only on one side of thevane part 11. Alternatively, however, the adjustable vane 1 may be of aso-called double shaft type or center type that has the shaft parts 12on both sides of the vane part 11.

Next, the frame base 2 will be described. The frame base 2 is a framemember that rotatably holds the plurality of adjustable vanes 1. Forexample, as shown in FIG. 1, the frame base 2 comprises an attachmentframe base part 21 and an opposite frame base part 22 arranged to holdthe adjustable vanes 1 (vane parts 11) therebetween.

The attachment frame base part 21 has an opening formed at the centerthereof and bearing parts 23 formed at regular intervals in thesurrounding area of the opening to receive the shaft parts 12 of theadjustable vanes 11. The adjustment mechanism 3 described later isarranged around the attachment frame base part 21.

The opposite frame base part 22 has the shape of a circular disk havingan opening at the center thereof as shown in FIG. 1, for example.

The distance between the attachment frame base part 21 and the oppositeframe base part 22 is substantially kept constant (of the order of thewidth h of the adjustable vane 1) so that the adjustable vanes 1 heldbetween the parts can smoothly rotate. For example, four caulking pins24 are provided on the outer side of the bearing parts 23 to maintainthe distance between the parts. A hole formed in the attachment framebase part 21 and the opposite frame base part 22 to receive the caulkingpin 24 is referred to as a pin hole 24P.

Next, the adjustment mechanism 3 including the lever plate 5 accordingto the present invention will be described. The adjustment mechanism 3is intended to appropriately rotate the adjustable vanes 1 to adjust theexhaust flow rate. For example, as shown in FIG. 1, the adjustmentmechanism 3 primarily comprises a drive ring 31 that produces arotational movement in the exhaust guide assembly AS and the lever plate5 that transfers the rotational movement to the adjustable vanes 1.

The drive ring 31 has a number of driving engaging parts 33 formed inthe periphery thereof that have the shape of a notch, for example, asshown in the drawing. The lever plate 5 is engaged with the drivingengaging part 33 so that the rotational movement of the drive ring 31 istransferred to the lever plate 5.

The drive ring 31 has an input part 36 having the shape of a U-shapednotch at which the drive ring 31 receives the driving force from anactuator AC.

As can be understood from the above description, the lever plate 5 isinterposed between the drive ring 31 and the shaft part 12 of theadjustable vane 1 to rotate the adjustable vane 1.

Next, the lever plate 5 will be described in detail.

As shown in FIG. 2, the lever plate 5 has an elongated plate main body51, a fitting hole 52 into which the shaft part 12 of the adjustablevane 1 is fitted formed in the plate main body 51 at a position close toone end thereof, and an engaging protrusion 53 to be engaged with thedrive ring 31 formed on the plate main body 51 at the end thereofopposite to the fitting hole 52.

The plate main body 51 is an elongated plate main body that is somewhatconstricted at the middle part thereof. The plate main body 51 has athickness t2 that is substantially equal to the thickness t1 of a blankworkpiece 5A, which is a material of the plate main body 51, asdescribed later. The thickness t1 can be approximately 40% to 70% of thethickness t0 of the conventional lever plate 105 shown in FIG. 8described above.

The fitting hole 52 formed at one end of the plate main body 51 has asubstantially rectangular shape in a plan view to conform to the shapeof the cross section of the shaft part 12 of the adjustable vane 1 thathas the opposite reference surfaces 15 at the end thereof.

The engaging protrusion 53 formed on the plate main body 51 at the endopposite to the fitting hole 52 is formed by bending the blank workpiece5A having the shape of an elongated plate. More specifically, the blankworkpiece 5A having the thickness of the plate main body 51 is bent andraised at that end part, and the raised end part is then compressed inthe direction of raising thereof. As a result, the engaging protrusion53 has a thickness t3 larger than the thickness t2 of the plate mainbody 51.

A side periphery 530 of the engaging protrusion 53 is subjected tofinish blanking to have an arc shape in a plan view. The arc-shaped sideperiphery 530 abuts against the driving engaging part 33 of the drivering 31 to transfer power.

The lever plate 5 according to the present invention is configured asdescribed above and is manufactured by a manufacturing method includingthe steps described below.

In the following, the manufacturing method will be described step bystep with reference to FIG. 3.

(i) Blanking Step

An austenite-based heat resisting steel suitable for the servicecondition is used as the starting material of the lever plate 5, and theelongated blank workpiece 5A is punched out of the starting material.

For ease of understanding of the principle, FIG. 3 shows one lever plate5 as being separately worked. However, as shown in FIG. 4, a pluralityof blank workpieces connected to each other can also be used in the caseof progressive working. In the blanking step, an uncompleted engagingprotrusion part 53A that is to form the engaging protrusion 53 is formedon one end of the blank workpiece 5A, the remaining relatively long partof the blank workpiece 5A is an uncompleted plate main body 51A, and theuncompleted engaging protrusion part 53A and the uncompleted plate mainbody 51A are flush with each other.

(ii) Bending Step

In the bending step, the uncompleted engaging protrusion part 53A of theblank workpiece 5A in the blanking step is bent and raised atapproximately 90 degrees from the initial position to form a bentintermediate workpiece 5B. The raised part that is to form the engagingprotrusion 53 is shown as an uncompleted engaging protrusion part 53B.The outer periphery of the bent part of the uncompleted engagingprotrusion part 53B is slightly rounded rather than right angled.

The uncompleted engaging protrusion part 53B in the bending step mayhave the thickness t1 of the material or the thickness t2 of the platemain body.

(iii) Crushing Step

In the crushing step, the uncompleted engaging protrusion part 53B bentin the preceding step is worked to have a reduced length and anincreased thickness to provide a crushed intermediate workpiece 5C. Morespecifically, the uncompleted engaging protrusion part 53B is crushedfrom above with a fine blanking die, a simple press die or an upsettingheader die to apply plane strain compression to the material. As aresult, the part of the material is deformed in a direction to increasethe plate thickness or in a direction toward the side periphery, and therounded outer periphery of the bent part is worked to have a rightangle. FIG. 3( iii) shows the deformed part as an uncompleted engagingprotrusion part 53C.

A specific example in which the working is performed by closed planestrain thickening press molding based on the fine blanking will bedescribed. This working is performed with a so-called upsetting die thatrestricts the finished shape, at room temperatures, with a ratio ofdimension change due to compression, that is, a press ratio or anindentation ratio v, ranging from 0.3 to 0.7. In the case where theblank workpiece is made of an austenite-based heat resisting steel, theproductivity and the product performance can be improved by heating theatmosphere to a temperature of 50 degrees C. to 200 degrees C.

When the thickness t2 of the plate main body 51 needs to be preciselyachieved, the part can also be pressed.

(iv) Finish Blanking and Piercing Step

In the finish blanking and piercing step, the planar contour of thecrushed intermediate workpiece 5C obtained in the previous crushing stepis trimmed, and at the same time, the fitting hole 52 is formed bypiercing, thereby obtaining the completed lever plate 5.

More specifically, the plate main body 51 is somewhat constricted at themiddle part thereof to reduce weight, and the engaging protrusion 53,especially the side periphery 530 thereof, is rounded. And at the sametime, the fitting hole 52 is formed by piercing. The engaging protrusion53 and the fitting hole 52 are formed with the positional relationshipbetween a fitting hole center C1 and an engaging protrusion center C2being precisely defined by the die, the fitting hole center C1 being theposition of an axis of the fitting hole 52, and the engaging protrusioncenter C2 being the position of an axis of the engaging protrusion 53.The completed lever plate 5 is manufactured in this way.

Finish blanking and piercing are preferably performed at the same time.However, as shown in FIGS. 3( iv)-(a), (b) and (c), after the crushingstep, a finish blanking step may be first singly performed. After that,the contour of the plate main body 51 may be trimmed, and the sideperiphery 530 of the engaging protrusion 53 may be rounded, and then,the fitting hole 52 may be formed by piercing in a remaining workingstep.

Alternatively, a piercing step may be first performed, and then, finishblanking may be performed in a remaining working step to complete theproduct.

In this way, the lever plate 5 described above is completed.

In the following, advantages of the lever plate 5 thus manufacturedowing to the working process will be described.

First, relationships between the bending and crushing(pressing/compression) and the weight and plate thickness will bedescribed based on a schematic analysis, and weight reduction achievedby the present invention will be described.

To facilitate understanding of the principle, the following discussionwill be made on the assumption that the lever plate is formed by acombination of rectangular parallelepipeds as shown in FIG. 5, forexample. FIG. 5( a) shows the lever plate according to the presentinvention, FIG. 5( b) shows a conventional lever plate.

The weight W₀ of the conventional lever plate is expressed as follows.

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack & \; \\\begin{matrix}{W_{0} = {\left( {{l_{0}w_{0}t_{0}} + {H_{0}w_{0}t_{0}} - {\pi \; {Rt}_{0}}} \right)\rho}} \\{= {{t_{0}\left( {{l_{0}w_{0}} + {H_{0}w_{0}} - {\pi \; R}} \right)}\rho}}\end{matrix} & (1)\end{matrix}$

The weight W₁ of the lever plate according to the present invention isexpressed as follows.

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack & \; \\\begin{matrix}{W_{1} = {\left( {{l_{0}w_{0}t_{1}} + {H_{0}w_{0}t_{1}} - {\pi \; {Rt}_{1}}} \right)\rho}} \\{= {{t_{1}\left( {{l_{0}w_{0}} + {H_{0}w_{0}} - {\pi \; R}} \right)}\rho}}\end{matrix} & (2)\end{matrix}$

The weight difference ΔW (=W₀-W₁) is expressed as follows.

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 3} \right\rbrack & \; \\{{\begin{matrix}{{\Delta \; W} = {W_{0} - W_{1}}} \\{= {\left\{ {{\left( {t_{1} - t_{0}} \right)\left( {{l_{0}w_{0}} - {\pi \; R}} \right)} + {\left( {{H_{0}t_{0}} - {H_{1}t_{1}}} \right)w_{0}}} \right\} \rho}} \\{= {\left( {t_{1} - t_{0}} \right)\left( {{l_{0}w_{0}} - {\pi \; R}} \right)\rho}}\end{matrix}\because{H_{0}t_{0}}} = {H_{1}t_{1}}} & (3)\end{matrix}$

The pressing ratio (indentation ratio) ν and a thickening ratio μ areexpressed as follows, on the assumption that the part to form theengaging protrusion 53 according to the present invention having theheight H1 and thickness t1 has a height H and a thickness t at the timeof pressing.

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 4} \right\rbrack & \; \\{{{{pressing}\mspace{14mu} {ratio}\mspace{14mu} \nu} = {\frac{H_{1} - H}{H_{1}} = {1 - \frac{H}{H_{1}}}}}{H = {H_{1}\left( {1 - \nu} \right)}}} & (4) \\\left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack & \; \\{{{{thickening}\mspace{14mu} {ratio}\mspace{14mu} \mu} = {\frac{t - t_{1}}{t_{1}} = {\frac{t}{t_{1}} - 1}}}{t = {t_{1}\left( {1 + \mu} \right)}}} & (5)\end{matrix}$

If it is assumed that the weight W₀ is fixed (closed plane strainpressing with fixed plate width is applied in the present invention),the following relation holds.

[Formula 6]

H₁t₁w₀=Htw₀  (6)

This expression is transformed to the following expression.

[Formula 7]

H₁t₁=Ht  (7)

Substituting the above formulas for H and t expressed by ν and μ into Hand t in this expression yields the following expression.

[Formula 8]

H ₁ t ₁ =H ₁(1−ν)·t ₁(1+μ)  (8)

[Formula 9]

∴(1−ν) (1+μ)=1  (9)

Therefore, the height H and the thickness t can be expressed by thepressing ratio (indentation ratio) ν as follows.

[Formula 10]

H=H ₁(1−ν)  (10)

The pressing ratio (indentation ratio) ν satisfies the followingrelation.

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 11} \right\rbrack & \; \\{t = \frac{t_{1}}{1 - \nu}} & (11)\end{matrix}$

In addition, according to the present invention, the following relationholds.

[Formula 12]

0<ν<1  (12)

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 13} \right\rbrack & \; \\\left. \begin{matrix}{{thickness}\mspace{14mu} {of}\mspace{14mu} {flat}\mspace{14mu} {plate}\mspace{14mu} {main}\mspace{14mu} {body}\text{:}\mspace{14mu} {t_{1\mspace{14mu}}\left( {\text{<}\mspace{14mu} t_{0}} \right)}} \\\begin{pmatrix}{t_{0}\mspace{14mu} {represents}\mspace{14mu} {thickness}\mspace{14mu} {of}\mspace{14mu} {conventional}} \\{{lever}\mspace{14mu} {plate}}\end{pmatrix} \\{{thickness}\mspace{14mu} {of}\mspace{14mu} {bent}\mspace{14mu} {and}\mspace{14mu} {raised}\mspace{14mu} {part}\text{:}\mspace{14mu} t\mspace{14mu} \left( {\text{>}\mspace{20mu} t_{1}} \right)} \\({controllable}) \\{{height}\mspace{14mu} {of}\mspace{14mu} {bent}\mspace{14mu} {and}\mspace{14mu} {raised}\mspace{14mu} {part}\text{:}\mspace{14mu} H\mspace{14mu} \left( {\text{>}\mspace{14mu} H_{1}} \right)} \\({controllable})\end{matrix} \right\} & (13)\end{matrix}$

FIG. 6 shows a change in weight of the lever plate indicated by theexpression (3) and changes in thickness and height of the raised partindicated by the expressions (10), (11), (12) and (13) compared with theconventional lever plate.

In FIG. 6, the relationship between the weight difference ΔW and thethickness difference (t_(0-t) ₁) is represented by a straight line thatpasses through the origin (where the thickness of the lever plateaccording to the present invention equals to the thickness of theconventional lever plate) and has a gradient θ indicated by tanθ=(I₀W₀-πR)ρ, where π is a constant, ρ is a specific gravity thatdepends on the material, and the remaining values depend on thespecifications according to the present invention and are controllable.The weight difference ΔW has a limit value ΔW_(lim)=(I₀W₀-πR) ρ whent₁=0.

As can be seen from FIG. 6, the decrease in weight (ΔW) assumes apositive value, and therefore, the lever plate according to the presentinvention has a reduced weight compared with the conventional leverplate.

Next, relationships between the plate thickness of the blank workpieceand the height H and pressing ratio (indentation ratio) ν of theengaging protrusion (uncompleted) will be described with reference toFIG. 7.

According to the present invention, a material having smaller thicknessthan conventional is used. In the closed plane strain thickeningpressing based on the fine blanking, for an appropriate height H₁ of theraised part changed from the height H₀ of the raised part of theconventional lever plate, the thicknesses of the flat part to be piercedand the uncompleted engaging protrusion part (t₁, t) satisfy therelations t₁<t₀ (flat part) and t>t₁. Both the thickness t and theheight H can be controlled by controlling the pressing ratio(indentation ratio) ν as the height H₁ changes. The inventor has foundand demonstrated that, although the pressing ratio (indentation ratio) νfor the austenite-based heat resisting steel is generally 0.5 at roomtemperatures, further pressing can be achieved by heating to 50 degreesC. to 200 degrees C. In the demonstration, a Formaster-typetemperature-controlled compression tester was used.

As a result of the demonstration experiment, the inventor has found thatthe Ludwick equation for work hardening of a material that is found incontraction flange deformation of γSUS and conventional elongationflange deformation.

σ′=K′ε′^(n′)  (14)

(σ′ and K′ represent the true stress and true strain of contractionflange deformation, and ε′ and n′ represent constant under the sameconditions)

These findings allow manufacture of the novel lever plate describedabove by a working method that can achieve the analysis result describedabove.

In particular, a characteristic of the method according to the presentinvention consists in press working of the engaging protrusion, and thecharacteristic provides an advantage. A material used in the presentinvention that is suitable for VGS is austenite-based heat resistingsteel. The material is bent and then worked by closed pressing, andtherefore, the product has been subjected to strong compressiondeformation. Since the recrystallization temperature of the material isabout 950 degrees C., and the service temperature thereof is about 800degrees C., the compressive strain is not easily released. Therefore,the abrasion resistance against sliding of a solid body at a hightemperature of about 800 degrees C. or against contact with the exhaustgas is improved.

The manufacturing method according to the present invention causes highcompressive work hardening in the lever plate 5, and the hightemperature hardening is maintained according to the temperaturerelationship described above. In practical use of a VGS typeturbocharger, high resistance against initial oxidation and initialabrasion is achieved.

REFERENCE SIGNS LIST

-   1 adjustable vane-   2 frame base-   3 adjustment mechanism-   5 lever plate-   11 vane part-   12 shaft part-   13 flange part-   15 reference surface-   2 frame-   21 attachment frame base part-   22 opposite frame base part-   23 bearing part-   24 caulking pin-   24P pin hole-   3 adjustment mechanism-   31 drive ring-   33 driving engaging part-   36 input part-   5 lever plate-   5A blank workpiece-   5B bent intermediate workpiece-   5C crushed intermediate workpiece-   5D molded workpiece-   51 plate main body-   51A plate main body in blanking step-   51B plate main body in bending step-   51C plate main body in crushing step-   52 fitting hole-   520 pierced hole-   53 engaging protrusion-   53A uncompleted engaging protrusion part (in blanking step)-   53B uncompleted engaging protrusion part (in bending step)-   53C uncompleted engaging protrusion part (in crushing step)-   530 side periphery-   105 lever plate-   151 plate main body-   152 fitting hole-   153 engaging protrusion-   AC actuator-   AS exhaust guide assembly-   C turbocharger-   G exhaust gas-   T turbine rotor-   t0 (conventional) thickness-   t1 (material) thickness-   t2 (plate main body) thickness-   t3 (engaging protrusion part) thickness

1. A lever plate that is incorporated in an exhaust guide assembly in aVGS type turbocharger, the exhaust guide assembly allows an engine toachieve a high power even when the engine runs at a low speed byrotating a plurality of adjustable vanes arranged at positionssurrounding a turbine rotor by transferring a shifting of a drive ringto the adjustable vanes via lever plates, appropriately constricting arelatively small amount of exhaust gas discharged from the engine withthe adjustable vanes to increase the velocity of the exhaust gas,rotating the turbine rotor with the energy of the exhaust gas, andfeeding an amount of air equal to or larger than the amount of air fedby natural aspiration to the engine with a compressor directly connectedto the turbine rotor, wherein the lever plate is made of anaustenite-based heat resisting steel and has a fitting hole into which ashaft part of the adjustable vane is fitted formed at a position closeto one end of an elongated plate main body thereof and an engagingprotrusion to be engaged with the drive ring formed at the other endthereof, said engaging protrusion is formed by bending a blankingmaterial having the shape of an elongated flat plate, and the engagingprotrusion is pressed in a direction of raising thereof so as to have athickness greater than the thickness of the plate main body of the leverplate, and opposite side peripheries of the engaging protrusion aresubjected to finish blanking to have an arc shape.
 2. The lever plate ina VGS type turbocharger according to claim 1, wherein said fitting holeis formed by piercing at the same time as the finish blanking of saidengaging protrusion.
 3. A method of manufacturing a lever plate that isincorporated in an exhaust guide assembly in a VGS type turbocharger,the exhaust guide assembly allows an engine to achieve a high power evenwhen the engine runs at a low speed by rotating a plurality ofadjustable vanes arranged at positions surrounding a turbine rotor bytransferring a shifting of a drive ring to the adjustable vanes vialever plates, appropriately constricting a relatively small amount ofexhaust gas discharged from the engine with the adjustable vanes toincrease the velocity of the exhaust gas, rotating the turbine rotorwith the energy of the exhaust gas, and feeding an amount of air equalto or larger than the amount of air fed by natural aspiration to theengine with a compressor directly connected to the turbine rotor,wherein the lever plate is made of an austenite-based heat resistingsteel and has a fitting hole into which a shaft part of the adjustablevane is fitted formed at a position close to one end of an elongatedplate main body thereof and an engaging protrusion to be engaged withthe drive ring formed at the other end thereof, in a blanking step, ablank workpiece is obtained by punching an elongated flat plate out of amaterial having substantially the same thickness as the plate main body,then in a bending step, the elongated blank workpiece is bent and raisedat substantially 90 degrees at one end to form a bent intermediateworkpiece having an uncompleted engaging protrusion part, then in acrushing step, said uncompleted engaging protrusion part is compressedin a direction of raising thereof to make the thickness of the saiduncompleted engaging protrusion part greater than the thickness of theplate main body to form a crushed intermediate workpiece, then in afinish blanking step, a periphery of said crushed intermediate workpieceis shaped by ironing to have the shape of a completed product to form ashaped workpiece, and in a piercing step that precedes, is performed atthe same time with or follows said finish blanking step, the fittinghole is formed by piercing in the plate main body at a position close tothe end opposite to the engaging protrusion to provide the completedproduct.
 4. The method of manufacturing a lever plate in a VGS typeturbocharger according to claim 3, wherein said finish blanking step andsaid piercing step are performed at the same time using the same die. 5.The method of manufacturing a lever plate in a VGS type turbochargeraccording to claim 4, wherein in said finish blanking step, oppositeside peripheries of the engaging protrusion formed on the crushedintermediate workpiece are worked to be an arc-shaped surface.
 6. Themethod of manufacturing a lever plate in a VGS type turbochargeraccording to claim 3, wherein in said finish blanking step, oppositeside peripheries of the engaging protrusion formed on the crushedintermediate workpiece are worked to be an arc-shaped surface.